Economics of distribution of agricultural chemicals, such as herbicides in general and glyphosate formulations in particular, can be much improved through provision of a high “loading” of active ingredient in the formulation, that is, the amount of active ingredient that can be accommodated in a container of given capacity.
Glyphosate is an acid that is relatively insoluble in water (1.16% by weight at 25° C.). For this reason it is typically formulated as a water-soluble salt in aqueous solution. A useful alternative is to prepare glyphosate as a dry salt in powder or granular form. For example, a dry water-soluble granular formulation of glyphosate ammonium salt can have a glyphosate acid equivalent (a.e.) content as high as about 86% by weight. This would appear at first sight to provide an excellent solution to the challenge of packing more glyphosate into a container of given capacity. Unfortunately the benefit of a dry glyphosate formulation in this regard is more limited than one might expect, because such a formulation tends to have low bulk density. Also, many end-users and many distributors prefer a liquid product because of flexibility in handling, thus a need remains for high-loaded liquid formulations of glyphosate.
U.S. Pat. No. 6,544,930 to Wright discloses an approach to meeting this challenge. According to this approach, a concentrated aqueous solution of glyphosate, predominantly in the form of one or a mixture of the potassium and monoethanolammonium (MEA) salts thereof, was provided, it having been determined that such a solution had an unexpectedly high specific gravity, permitting more glyphosate a.e. to be delivered in a container of given capacity than was previously attainable using the isopropylammonium (IPA) salt in widespread commercial use, for example as Roundup® herbicide of Monsanto.
Unfortunately, glyphosate potassium salt, especially when formulated at high concentration in aqueous solution, brings some challenges of its own. For example, where (as often) it is desired to coformulate a surfactant with the glyphosate, physical incompatibility of the surfactant with the glyphosate salt can limit the options available. Whereas a range of surfactants are compatible with glyphosate IPA salt, fewer have been found to be compatible with glyphosate potassium salt, in particular where the salt is present at high concentration. See above-cited U.S. Pat. No. 6,544,930, col. 9, lines 6-13.
Another challenge arises where a user of a glyphosate potassium salt formulation wishes to add to that formulation, with dilution in water (for example in a spray tank) a second herbicide that is also in a form of a salt, for example a phenoxy-type herbicide salt such as an organic ammonium, illustratively dimethylammonium (DMA) salt of 2,4-dichlorophenoxyacetic acid (2,4-D), to form a tank mixture. Such tank mixtures of glyphosate and phenoxy-type herbicides are widely used, but their use can be limited by a tendency, under certain conditions, for precipitation of solids that can settle and clog filters or nozzles of field spraying equipment. This tendency is evidence of physical incompatibility of the glyphosate salt and the phenoxy-type herbicide salt under such conditions.
International Patent Publication No. WO 03/013241 proposes, inter alia, a glyphosate composition comprising IPA and potassium cations in a mole ratio of 1:10 to 30:1, “more preferably less than 15:1 and greater than 1:2”, reportedly as a means to improve bioefficacy over compositions of a single glyphosate salt.
U.S. Patent Application Publication No. 2003/0125209 states that viscosity of concentrated glyphosate IPA formulations can be reduced by using a lower molar excess of IPA than a 15-20% molar excess, said therein to be “typical”. A glyphosate/IPA mole ratio “between about 1.00:1.00 and about 1:00:1.10 . . . , preferably between 1:00:1.00 and about 1.00:1.05” is proposed therein.
Publications cited above are incorporated herein by reference.
Considering the variety of conditions and special situations under which glyphosate herbicides are used around the world, there remains a need for aqueous concentrate formulations of glyphosate, including surfactant-containing formulations, providing benefits under at least some of those conditions and situations. There is an especial need for such formulations having high glyphosate loading, for example at least about 400 g a.e./l, that are compatible when tank mixed with phenoxy-type herbicide salts under a wide range of field conditions.